<blockquote class=“Quote” rel=“joshua_segal”>I’m not sure if what LiftGuy said was true: Bromley, Killington and I am sure others, run their HSQs at less than full-speed on weekdays and at low volume times. I assume it is to save money as well as the wear and tear on the haul-rope going around the bull-wheel. If it were less efficient to run it slower, I suspect they wouldn’t.</blockquote>
It depends entirely on the type of lift. I think LiftGuy was referring specifically to the OP’s scenario at Alta. In that case, he’s right: fixed-grip lifts are not meant to be run at slow speeds for extended periods. Detachables are a different animal. Since the carriers are not on the line at the terminals, the speed factor is irrelevant in that sense. In fact, running detachables at a slower speed means fewer grip cycles, and therefore less wear & tear.
With respect to energy efficiency, it depends on the type of motor and drive. An old AC wound rotor induction motor would use resistor banks to reduce speed, making slow operation excessively inefficient. Long-term slow operation is even dangerous due to resistor heat. Until relatively recently ('05-ish), most big lifts were powered by DC motors with SCR (thyristor) drives. With these drives, power factor suffers when high torque is required at low speeds (high current, low voltage). In more modern large lifts, variable frequency drives power AC motors and can supply 100% torque across all speeds. These motors/drives can be operated efficiently at any speed.
Anyway… there’s a lot to it. In simple terms, fixed grip lifts like to run near their design speed. Detachables are more flexible about slower operation over long periods.
